AND HOW TO USE IT. 103 



Blue Emulsion (modified from Thiersch's formula) : — 



I. — To 300 ccm. of melted gelatine add 120 ccm. of a cold 

 saturated solution of green vitriol (ferro-sulphate). 



2. — To 600 ccm. of melted gelatine add, first, 240 ccm. of 

 a saturated solution of oxalic acid ; then 240 ccm. of a cold satu- 

 rated solution of red prussiate of potash (potassic ferryocyanide). 



3. — Pour No. I slowly into No. 2, stirring vigorously; the 

 mixture to be heated for fifteen minutes. 



4. — After cooling, press the emulsion through netting, the 

 strings washed, and spread on waxed paper for drying. In this 

 case these strings must be dried directly, as they do not melt well 

 without adding oxalic acid. 



The dry strings, or vermicelli, are prepared for use by first 

 soaking in cold water, and then heating with the addition of 

 oxaHc acid, enough to reduce them to a liquid. 



Black Emulsion.— (i) Soak 500 grms. gelatine in 2 litres of 

 water, in which 140 grms. of common salt have previously been 

 dissolved, and melt the mass on the water-bath. 



(2) Dissolve 300 grms. nitrate of silver in i litre distilled 

 water. 



(3) No. 2 poured very slowly into No. i while stirring. 

 An extremely fine-grained emulsion may be obtained by using 

 three or four times as much water in Nos. i and 2. 



(4) No. 3 pressed into vermicelli, as above, and then mixed 

 with No. 5 by clear daylight. 



(5) Mix li litres of cold saturated solution of potassic oxalate 

 with 500 ccm. of a cold saturated solution of ferro-sulphate. 



(6) No. 4, mixed with No. 6, gives a thoroughly black emul- 

 sion, which should be washed for several hours, again melted, 

 and finally poured in a thin layer on waxed paper. A grey-black 

 emulsion may be obtained by using 240 grms. potassic bromide in 

 the place of common salt in No. i, the remaining operations 

 being the same. 



A good mass for Ordinary Injections.— Dry starch ("laundry" 

 is good), I vol. ; 2^ per cent, aqueous solution of chloral 

 hydrate, i vol. ; 95 per cent, alcohol, \ vol. ; some colour, ^ vol. 

 (The chloral and alcohol prevent fermentation when mass is kept, 



